1June 7, 2004 Ontologies for interoperability 1

Ontology-based data integration

Maurizio LenzeriniDipartimento di Informatica e Sistemistica “A. Ruberti”

Università di Roma “La Sapienza”

DASI ’06: Phd School on Data and Service IntegrationBertinoro, December 11–15, 2006

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Data integration architecture

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Parameters

• Which Description Logic for the ontology• We will mention different possibilites

• Which language for user queries• Unions of conjunctive queries

• Which type of mapping• We will consider mappings of type GAV

• Which sources• Relational sources

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OWL-DLOWL concept constructors:

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OWL-DL

Types of axioms:

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The Description Logic DL-lite

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DL-lite

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DL-lite - example

Manages

Manages

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Dl-lite - semantics

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Results on data complexity

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A note on mappings

• In Ontology-based integration we have to deal with the “impedence mismatch” problem• Sources store data, while instances of concepts and relations

in the ontologies are objects

• The solution is to define a mapping language that allows specifying how to transform data into objects

• Basic idea: use “Skolem functions” in the head of the mapping

• Semantics: objects are denoted by “terms” (of exaclty one level of nesting), and different terms are different objects (unique name assumption on terms)

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Mappings: exampleThree sources on students: • s1 uses code for identifying students• s3 uses number for identifying • s2 stores (incomplete) correspondences between code and number

Student(sbc(code)) :- s1(code,dob,addr,city)Student(sbc(code)) :- s2(number,code)Student(sbn(number)) :- s3(number,addr,city), not s2(number,code)LivesIn(sbc(code),c(city)) :-s1(code,dob,addr,city), city is not nullLivesIn(sbc(code),c(city3)) :- s1(code,dob,addr,city1), city1 is null,

s2(number,code), s3(number,addr,city3), city3 is not nullLivesIn(sbc(code),c(city3)) :- not s1(code,dob,addr,city1),

s2(number,code), s3(number,addr,city3), city3 is not nullLivesIn(sbn(number),c(city)) :- s3(number,address,city), city is not null,

not s2(number,code)